Apparatus for cleaning mechanical devices using terpene compounds

ABSTRACT

Apparatus for cleaning printed wiring boards and/or printed circuit boards after soldering thereof for removal of rosin soldering fluxes using terpene compounds. The apparatus includes three separate components, a first housing containing the terpene washing apparatus, a second housing containing a water rinsing apparatus, and intermediate conveying means for transporting the devices from the first housing to the second housing. This intermediate conveying means should be disposed at an angle such that the end facing the second housing is disposed lower than the first end. Exhaust fans are provided for the first housing to prevent escape of terpene odors or vapors therefrom, while similar exhaust fans in the second housing prevent the escape of water vapor. Scrubbers are provided in the exhaust ducts from the first housing to prevent terpene compounds from escaping to the atmosphere. A flame detector prevents the introduction of boards having flames thereon or being overheated. A series of temperature controls prevent the terpene vapor temperature from rising above a predetermined value to prevent the vapors from igniting.

This application is a continuation of application Ser. No. 07/400,372,filed Aug. 30, 1989, now U.S. Pat. No. 5,103,846.

FIELD OF THE INVENTION

This invention relates generally to cleaning apparatus for mechanicaldevices, and more particularly to apparatus for cleaning printed circuitboards utilizing terpene compounds.

BACKGROUND OF THE INVENTION

In the fabrication of printed wiring boards and/or printed circuitboards, soldering is the preferred technique for electrically connectingcomponents. Soldering fluxes are first applied to the substrate boardmaterial to ensure firm, uniform bonding of the solder. While both rosinand non rosin soldering fluxes are available, rosin fluxes are preferredbecause they are less corrosive, and have a much longer history of use.The non-rosin, water soluble fluxes are a more recent development.However, these non rosin fluxes contain strong acids and/or aminehydrohalides and are thus corrosive, and can cause circuit failure ifresidual traces are not carefully removed. While batch type orunderbrush cleaners were initially employed, in-line solvent cleanerslater were adopted to meet demands of increased throughput. The removalof rosin fluxes from printed circuit boards or printed wiring boards hastraditionally been accomplished using chlorinated hydrocarbon andchlorofluorinated solvents such as 1, 1, 1,-trichlorethane,trichloromonofluoromethane, methylenechloride, trichlorotrifluoroethane,methylchloroform and CFC 113.

By the early 1970's aqueous cleaners using alkaline cleaning compoundssuch as the alkanol amines, usually in the form of monoethanolamine,were adopted for rosin flux removal as an alternative to the toxicchlorinated hydrocarbon and chlorofluorinated solvents. These aqueouscleaners chemically react with the rosin flux to form a rosin soapthrough the process of saponification. Other organic substances such assurfactants or alcohol derivatives may be added to these alkalinecleaning compounds to facilitate the removal of such rosin soap.Unfortunately, these compounds, like the water soluble soldering fluxes,have a tendency to cause corrosion on the surfaces and interfaces ofprinted wiring boards if they are not completely and rapidly removedduring the fabrication process.

With the advent of surface mounted devices which are soldered ontoprinted circuit boards using wave soldering or infrared solder reflowtechniques, chlorinated hydrocarbon and chlorofluorinated solvents wereonce again required to remove the rosin fluxes because of their lowcost, fast evaporation characteristics, and ability to clean underlightly spaced components. However, during the past few years, it hasbecome evident that chlorinated hydrocarbon and chlorofluorinatedsolvents are highly undesirable, because they are toxic, and their useis subject to close scrutiny by the Occupational Safety and HealthAdministration, and stringent containment equipment must be used.Moreover, if released into the environment, these solvents are notreadily biodegradable, and they are thus hazardous for long periods oftime. In particular, it has been discovered that chlorofluorocarbons areinstrumental in depleting the ozone layer in the earth's atmosphere.This awareness of the dangers of such solvents has driven a search forsafe, effective alternatives.

Alternatives which have emerged from this search are terpene compoundswhich have become increasingly popular in electronic cleaningapplications. The use of terpene compounds for cleaning mechanicaldevices has been known for many years. The United States Department ofAgriculture sponsored work on limonene and other citrus based terpenecompounds as long ago as the 1930's. However, there was very littleinterest in industrial uses of terpene compounds after that period oftime, because of the availability at very low cost of halogenatedsolvents and petroleum distillates. With the reawakening of interest interpene cleaners, it has been recognized that they provide a viablealternative to CFC's and other halogenated solvents for cleaning rosinfluxes from printed circuit boards. The use of one such terpene compoundwhich is sold under the trademark BIOACT EC 7 by Petroferm, Inc., forcleaning rosin fluxes, is the subject of U.S. Pat. No. 4,640,719 issuedon Feb. 3, 1987.

In some regards, such terpene compounds are ideal for the removal ofsolder fluxes. Their ability to clean even the most closely spaced SMTboards has been shown in tests, and such terpene compounds work wellwith all available flux types. Terpene compounds are also costcompetitive with most CFC's. Most terpene compounds are low in mamaliantoxicity, and many are recognized as safe for use as food additives. Inaddition, they are produced by nearly all living plants, and thereforeterpene compounds are ubiquitous components of the atmosphere for bothrural and urban areas. Plants, particularly coniferous forests, releasehundreds of millions of tons of terpene compounds into the air eachyear. In the atmosphere, terpene compounds are photochemically reactive.Wood and citrus products are the principal commercial sources of terpenecompounds. Some terpene compounds are used as extracted, but most ofthem are obtained from natural oil refining processes. As a result,terpene compounds are commercially available in huge volumes.

Terpene compounds are readily biodegradable, and both municipal andindustrial waste treatment facilities are normally able to handleterpene biodegradable without difficulty. Naturally derived terpeneproducts contain no carbon chlorine bonds, and it is the absence of suchcarbon chlorine bonds which are hard for biological systems tometabolize which renders terpene compounds so readily biodegradable.Terpene compounds can work at low temperatures, such as roomtemperatures, so it is not necessary to heat terpene cleaning baths.Terpene compounds are not volatile and have boiling points far abovethose of halogenated solvents. Also, most terpene compounds have a veryhigh relative dissolving ability, sometimes even greater than that ofany halogenated solvent.

Despite the foregoing characteristics of terpene compounds, they haveyet to emerge as a commercially acceptable substitute for chlorinatedand chlorofluorinated solvents. One reason is that most commerciallyavailable terpene compounds have flash points in the range of between100° F. and 200° F. which causes them to be classified as combustiblesubstances. This shortcoming must be taken into account in theproduction of any commercial machinery utilizing them as solvents forcleaning printed circuit boards. Another problem is the odor associatedwith most terpene compounds. Limonene is the terpene hydrocarbon mostoften used in cleaning products available in the market today. Thismaterial is derived from citrus by-products, such as oranges. Theresulting odor, when concentrated, is pungent. A third problem is that,unlike chlorinated and chlorofluorinated solvents and petroleumdistillates, terpene compounds are not volatile, so they will notevaporate. Therefore, they must be removed by rinsing. However, ifterpene compounds are mixed with small amounts of water, they can turnto a gel and become useless. Finally, these terpene compounds tend to bevery aggressive, precluding the use of certain elastomer materials interpene cleaning systems.

It is therefore an object of the present invention to provide apparatusfor the rapid, in line cleaning of printed circuit boards using terpenecompounds.

It is another object of the present invention to provide apparatus forcleaning printed circuit boards which uses terpene compounds and whichis safe for use with materials having flash points within the range of100° to 200° F.

It is a further object of the present invention to provide apparatus forcleaning printed circuit boards which uses terpene compounds and whichminimizes odor emissions to the atmosphere, and to the surroundingenvironment.

It is yet another further object of the present invention to provideapparatus for cleaning printed circuit boards which uses terpenecompounds and which also employs a water rinse.

It is yet another further object of the present invention to provideapparatus for cleaning printed circuit boards which uses terpenecompounds and which is safe for use in industrial environments.

SUMMARY OF THE INVENTION

These and other objects are achieved by the present invention whichrelates to apparatus for cleaning soldering fluxes from printed wiringboards and/or printed circuit boards using terpene compounds. Theapparatus of this invention comprises three separate and distinctcomponents, terpene compound washing apparatus, unloading apparatus, andwater rinsing apparatus. Each component includes a product conveyorwhich is physically separated from the conveyors of the othercomponents. In the washing apparatus, nozzles are used to spray theboards with a solution which typically includes a terpene compoundcombined with one or more terpene emulsifying surfactants. The unloadingapparatus carries the boards from the washing apparatus to the rinsingapparatus. In the rinsing apparatus the terpene solution is removed fromthe boards by water sprayed through nozzles as the board passestherethrough.

The problem of terpene removal without contamination of the terpene bathis overcome by physically separating the rinsing apparatus from thewashing apparatus by a separate and distinct unloading apparatus inwhich the conveyor is disposed at an angle with respect to thehorizontal such that the end of the unloading conveyor adjacent therinsing apparatus is lower than the end adjacent the washing apparatus.In this manner, water which inadvertently is splashed onto the unloadingapparatus conveyor will be conducted by gravity downwardly back towardthe rinsing apparatus, and not to the washing apparatus. Furthermore,the conveyors used for each apparatus are separate and are notphysically connected, so no water is carried by the conveyors from therinsing apparatus to the washing apparatus. Also, flexible baffles areplaced along the entrance to the rinsing apparatus, so that water in therinsing apparatus will not splash onto the conveyor of the unloadingapparatus. Finally, to minimize the escape of water vapor or waterdroplets from the rinsing apparatus during operation, an exhaust ductcoupled to a strong exhaust fan is disposed within the rinsing apparatusadjacent the entrance thereof. Another such exhaust duct may be placedadjacent the exit to the rinsing apparatus for the same purpose.

The odor problem associated with terpene compounds is overcome by theprovision of a similar set of exhaust ducts within the washing apparatusadjacent the entrance and exit thereto. An exhaust fan is coupled toboth ducts, drawing air through the entrance and exit to the washingapparatus, and exhausting gases from the interior of the washingapparatus. Disposed within the exhaust ducts are scrubbers, each ofwhich includes a water rinse system. In addition, a hood is placed overeach of the entrance and exit to the washing apparatus, which, whencoupled with the strong air flow created by the exhaust fan, minimizesthe escape of fumes from the interior of the washing apparatus.

The use of stainless steel for all components of the apparatus overcomesthe problem of the aggressive nature of the terpene compounds.

A number of safeguards have been provided in the present invention toaccommodate the low flash point of terpene compounds. Typically, in thewashing apparatus, the terpene compound is disposed in an open bathbeneath the conveyor carrying the printed circuit boards which are to becleaned. The exhaust ducts previously described provide continualventilation above the bath, preventing the build up to dangerous levelsof vapors. Cooling coils are disposed within the terpene bath, and atemperature sensor maintains the bath temperature within a desiredrange. This temperature sensor automatically shuts off the washingapparatus if the bath temperature exceeds a predetermined value. In analternative embodiment, a redundant temperature sensor in the terpenebath provides a back up, in case the first sensor fails. In addition,one or two other temperature sensors are disposed above the bath. Thesetemperature sensors are pre programmed to release carbon dioxide intothe space above the bath, should the temperature exceed a predeterminedvalue, to suppress any potential fire hazard.

Another concern is that because the washing apparatus often is disposeddirectly in line with the high temperature soldering apparatus, it hasbeen suggested that boards leaving the soldering apparatus and enteringthe washing apparatus may be involved in flames. Obviously, it would beundesirable if such a board entered the washing apparatus. To preventsuch a possibility, a flame detector is disposed at the entrance to thewashing apparatus and to immediately shut down the washing apparatusshould a flame be detected on an entering board.

Air flow and water flow detectors are disposed in both scrubbers, sothat if sufficient exhaust flow is not present, or if sufficient waterflow for washing the scrubbers is not present, the washing apparatuswill be shut off.

In addition to the foregoing, an automatic loading apparatus can beprovided prior to the washing apparatus, for automatically transferringprinted circuit boards from a soldering operation directly to theentrance to the washing apparatus. Alternatively, the boards can beloaded by hand, if desired. In a preferred embodiment, an air knife isdisposed at the end of the washing apparatus but prior to the unloadingapparatus for removal of some, but not all of the terpene compoundsolution. A dryer is provided within the rinsing apparatus for removalof water from the boards.

In an alternative embodiment, windows with locks are provided along thetop of the washing apparatus. Sensors are provided indicating whetherthe window is in a locked position. The washing apparatus cannot beactivated until all windows are locked.

The foregoing apparatus overcomes the problems associated with the useof terpene compounds for washing rosin soldering fluxes from printedwiring boards and/or printed circuit boards, and permits the washing ofsuch boards on an assembly line basis in an in line configuration withan existing soldering system.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects, advantages and features of this invention will be moreclearly appreciated from the following detailed description taken inconjunction with the accompanying drawings in which:

FIG. 1 is a perspective view of the apparatus of this invention;

FIG. 2 is a perspective view of the interior of the apparatus of FIG. 1of this invention;

FIG. 3 is a cutaway, side plan view of the apparatus of FIG. 1;

FIG. 4 is a partially cutaway, top plan view of the apparatus of FIG. 1;

FIG. 5 is a cutaway, end plan view of the apparatus of FIG. 1 taken fromthe left end as shown in FIG. 1;

FIG. 6 is a partial top, perspective view of the windows of theapparatus of FIG. 1; and

FIG. 7 is a partial cross-sectional side plan view of the window locksof FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference now to the drawings, and more particularly to FIGS. 1-3thereof, cleaning apparatus 10 of this invention will be described.Cleaning apparatus 10 includes washing apparatus 12, unloading conveyorassembly 14 and rinsing apparatus 16. Typically, conveyor assembly 14,washing apparatus 12, and rinsing apparatus 16 are disposed in anin-line relationship to permit the automatic transfer of boards fromapparatus 12 to assembly 14 and to rinsing apparatus 16 without need ofany human intervention.

Washing apparatus 12 will now be described with particular reference toFIGS. 1-3. Washing apparatus 12 includes a housing 26 through which aconveyor 20 passes from an inlet 18 to an outlet 22, spraying apparatus24 disposed within housing 26, and exhaust system 28. Spraying apparatus24 includes a bath 32 of a washing compound, sprayers 34, and at leastone pump 36 for pumping the washing compound from bath 32 to sprayers 34through conduits 38.

The washing compound in bath 32 comprises a terpene compound, preferablycombined with one or more terpene emulsifying surfactants to facilitatethe removal of the terpenes from printed circuit boards when rinsed withwater. Terpene compounds which are suitable for this purpose include,but are not limited to, pinene, both alpha and beta isomers, qammaterpinene, delta--3--carene, limonene and dipentene. Preferred terpenecompounds are limonene and dipentene. A preferred, commerciallyavailable product is sold under the trademark BIOACT EC-7 by Petroferm,Inc, of Fernandina Beach, Fla. 32034. Numerous surfactants are capableof emulsifying the terpenes of this invention, and include, but are notlimited to the linear alkyl benzene sulfonates, linear or branched chainalcoholic ethoxylates and ethoxysulfates, polysorbate esters,ethoxylated alkylphenols and alkyl and dialkyl sucoinate compounds. Anexample of the latter class of compounds is sodium dioctylsulfosuccinate. The ethoxylated alkylphenols contain various alkyl sidechains and various numbers of linked ethylene oxide units. Usefulcompounds of this class contain from about 5 to about 20 ethylene oxidegroups, with 7 or 8 being preferred. The quantity of terpene emulsifyingsurfactants in the compositions of the present invention may range on aweight basis from 0 to about 40%, with the terpene compounds accountingfor the balance of the compositions. Useful terpene compounds, andsurfactants, and methods for their use are set forth in U.S. Pat. No.4,640,719.

Bath 32 typically resides within the lower portion of an interior cavity27 defined by housing 26. Conveyor 20 passes directly over bath 32 sothat liquid which is emitted by sprayers 34 passes through conveyor 20and immediately returns to bath 32. Conveyor 20 is typically formed ofan open mesh which has openings sufficiently small to prevent printedcircuit boards from falling therethrough, but large enough to allowliquid to readily pass through. Thus, very little of the washingcompound is removed from washing apparatus 12. This is important, sincethe washing compound of bath 32 is expensive.

Sprayers 34 may be any known, commercially available sprayer suitablefor use with highly aggressive compounds, and each sprayer typicallyincludes tube 40 and nozzles 42. Tubes 40 each have a plurality ofnozzles 42 disposed on aside thereof facing conveyor 20 and preferablyare oriented transversely of the direction of conveyor 20. One or morepumps 36 supply compound to nozzles 42 from bath 32 through one or moreconduits 38. Each nozzle 42 preferably provides a spray which strikesthe board at an angle with respect to the vertical. While the spacing ofconveyor 20 from sprayer 34 is not critical, it should be sufficientlygreat to permit the printed circuit boards with components mountedthereon to pass between sprayers 34 and conveyor 20. However, it shouldnot be so great that the intensity and velocity of the spray emitted bynozzles 42 is excessively diminished when striking the surface of theboard. Although sprayers 34 are shown disposed both above and belowconveyor 20, the sprayers below conveyor 20 are optional.

Nozzles 42 are arranged in an array such that the spray from nozzles 42covers the entire lateral surface of conveyor 20 and a substantialportion of the length of conveyor 20 within cavity 27. It is desiredthat the spray from nozzles 42 on the top sprayer 34 strikes the boardwith sufficient intensity and at a sufficient angle that the washingcompound penetrates into the small space between the components and theprinted circuit board. A typical component clearance on the board is inthe range of about 0.003 to about 0.008 inches, and nozzles 42 must becapable of forcing liquid into this space. In a preferred embodiment,the manifold pressure of the spray is in the range from about 20 toabout 40 psi with 25 psi being preferred. Nozzles 42 preferably,although not necessarily, are disposed at an angle 41 with respect tothe vertical. A preferred angle 41 is in the range of from about 10° to25° with respect to the vertical. Typically nozzles 42 expel afan-shaped spray which subtends an angle 43 of from about 10° to about25°, with 15° to 20° being preferred. In a typical apparatus 12, theflow volume through sprayers 34 is about 180 gallons per minute ofworking compound.

Exhaust system 28 prevents the escape of vapor, droplets and odor fromwithin housing 26, during operation of the apparatus. Exhaust system 28includes exhaust ducts 44 and 46, exhaust fan 48 and scrubbers 50. Duct44 has an opening 52 disposed closely adjacent inlet 18, while duct 46has an opening 54 disposed closely adjacent outlet 22. In this manner,negative pressures are created at both inlet 18 and outlet 22 whichmakes it difficult if not impossible for the escape of vapors, waterdroplets or odors. A single fan 48 can be used for both ducts 44 and 46or a separate fan can be used for each duct. Reflective openings 52 and54 of ducts 44 and 46 typically are disposed above top sprayers 34 andconveyor 20 closely adjacent inlet 18 and outlet 22 respectively.Preferably, a baffle 49 is disposed around each of openings 52 and 54and extends across the width of conveyor 20. Baffle 49 includes a narrowslotted opening 47 which evenly draws air from across the width ofconveyor 20.

Scrubbers 50 prevent the escape of combustible liquids, vapors, andodors to the outside atmosphere. An identical scrubber 50 is disposed ineach of ducts 44 and 46. Scrubber 50 is disposed somewhere betweenopening 52 or 54 and fan 48. Typically, scrubber 50 includes means 56for removing terpene vapor and droplets from the exhaust airstream,means 58 for washing means 56, drain 60 for removing the fluid from thewashing means 58, a water flow detector 62 and an air flow detector 64.Scrubbing means 56 can include any material commonly used for theremoval of vapor and droplets from an exhaust air stream. A preferredmaterial is a plurality of polypropylene saddles 66 which ar held inplace within ducts 44 or 46 by upper retainer 68 and lower retainer 70.Retainers 68 and 70 typically are an mechanical device which permits airand water to flow therethrough, while preventing saddles 66 from fallinginto drain 60. A typical example is a plurality of rods criss-crossingin the center of ducts 44 or 46. Washing means 58 typically includes anozzle 72 and a pipe 74 which is coupled to a source (not shown) ofwashing fluid. Typically, water is used as the washing fluid, and pipe74 is coupled to a water supply. Nozzle 72 sprays scrubbing means 56 towash the combustible vapors and liquids therefrom down drain 60. Opening52 should be spaced sufficiently far from washing means 58 that waterused in the washing operation does not work its way into bath 32.Typically, connecting duct 45 coupling opening 52 to duct 44 is angledslightly downwardly away from opening 52 to prevent water from runningdown duct 45 into bath 32 (See FIG. 5).

A hood 76 is disposed around inlet 18, while a hood 78 is disposedaround outlet 22. Hood 76 has an associated narrow opening 80 throughwhich conveyor 20 passes, and into which the printed circuit boards areinserted. Similarly, hood 78 is provided with an opening 82 throughwhich conveyor 20 passes, and through which the printed circuit boardsexit. Both openings 80 and 82 should be narrowed to facilitate thecreation of negative pressure, and to enhance the rate of air flow fromthe exterior through inlet 18 and outlet 22 to make it more difficultfor the escape of vapor, droplets or odor. Obviously, both openings 80and 82 should be sufficiently large to allow conveyor 20 and printedcircuit boards thereon to pass therethrough.

At least one air knife 30 is provided after the last sprayer 34, butprior to outlet 22 and prior to opening 54. Preferably, an air knife 30is disposed both above and below conveyor 20. Air knife 30 typicallyincludes a plurality of nozzles 31 through which air is forced and whichare aligned transversely of the direction of movement of conveyor 20.Typically, air is forced through these nozzles 31 at a high pressure.Preferably, only one set of nozzles 31 is used, although a plurality oftransversely extending sets of nozzles 31 may be used in some instances.

The purpose of air knife 30 is to remove some of the washing compoundfrom the printed circuit boards and the devices mounted thereon.However, air knife 30 should not completely dry the boards. The boardsshould be left slightly damp, and some of the washing compound should beleft disposed in the narrow spacing between the board surface and thecomponents mounted thereon. By allowing some of the compound to remainin the spacing between the components and the board surface, water iswicked into the spacing during the rinsing, to allow the washingcompound, along with the excess rosin solder flux to the completelywashed off the board and out of the narrow spacings. It is the wettingproperties of the surfactants which permits this wicking to occur. Inthe absence of washing compound in these narrow spacings, it isdifficult to force water into the spacing to completely flush the area.However, some removal of the washing compound is required, to minimizethe escape of odor and fumes into the surrounding atmosphere during thecleaning process. Typically, the use of compressed air from one set ofnozzels at pressures in the range of from about 40 to almost 100 psiadequately removes the excess washing compound from, under and aroundthe components, but it does not remove all of the compound.

Several safety systems are included in washing apparatus 12 to preventany accidents resulting from the low flash point of the terpene compoundvapors. A cooling system is provided for bath 32. The cooling systemincludes a temperature sensor 84, cooling coils 86 and a coolant supplyline 88. Although heaters are neither used in the system nor required,heat generated by pumps 36 can raise the bath temperature by 40° F. orhigher. If the temperature of bath 32 exceeds about 80° F., the fluidshould be cooled. Sensor 84 senses the temperature of the bath, and whenthe temperature exceeds a pre-determined value, sensor 84 triggers theflow of coolant from a supply (not shown) through coolant supply line 88and into coils 86 disposed within bath 32. Typically, the coolant usedis water, and the water is circulated through coils 86 as needed tomaintain the bath temperature at the desired level.

The washing apparatus is frequently disposed in an in-line configurationwith a soldering apparatus, so that opening 80 of hood 76 accepts boardsdirectly from a conveyor 77 (FIG. 1) of a soldering apparatus, such as asolder reflow apparatus. Boards exiting the soldering apparatus areimmediately picked up by conveyor 20 and carried into hood 76. Dependingupon the reliability of the soldering apparatus, the boards, and thecomponents thereon, may be involved in flames. Because of the in-linepositioning of the washing apparatus, and because of the automatednature of the soldering procedure, the flames may go undetected. Thepresence of flames, or even an overly hot board within housing 26 couldbe dangerous, because of the low flash point of the terpene compoundvapors. Therefore, to prevent any accidental ignition of the terpenecompound vapors, a flame detector 90 is positioned within hood 76 atinlet 18. Flame detector 90 is positioned a sufficient distance from theinterior cavity 27 of housing 26 that the presence of flame, or anexcessively hot board, is detected before that board enters cavity 27.Flame detector 90 includes a core 91 within a housing 93 which formed ofa metal or some other material which melts at a predetermined, lowtemperature. Flame detector 90 ca be any conventional commerciallyavailable device used for such purposes, and typically is an eutecticsalt detector. An acceptable, commercially available detector can beobtained from Walter Kidde Co., and includes a KIC-100 Control Unit.When the predetermined melting temperature of this material is exceededby heat produced by the flame or by some other heat source on conveyor20, core 91 melts, interrupting the flow of a current through flamedetector 90. This current interruption immediately disables the washingapparatus 12, stopping conveyor 20 and pump 36 to terminate the sprayingactivity, and movement of printed circuit boards through housing 26. Inthis manner, any overheated board or one which is on fire will not entercavity 27, and there is no danger of any vapor ignition. Exhaust fan 48continues to run, drawing vapors from cavity 27 to prevent any vaporbuild up during the period of shutdown.

An alternative embodiment of the flame detector is shown in FIG. 5. Acommercially available photo ionization detector 97 can be mounted at astrategic location within cavity 27 at a point where flaimes at inlet 18can be detected. Detector 97 illustratively is shown mounted at opening52 in FIG. 5 and pointed toward inlet 18. Detector 97 also disableswashing apparatus 12 to shut down conveyor 20 and pump 36. Acommercially available example is a UV TRON R2868, sold by Hamamatsu.

Sensor 84 in bath 32 also provides an over temperature control. Sensor84 is coupled to control panel 92. If the temperature of bath 32 exceedsa preset value, as measured by sensor 84, pump 36 and conveyor 20 aredisabled, stopping the washing and conveying operation. In this manner,operation is terminated well before the vapor flash temperature isreached. Typically, the bath temperature which triggers the shutdown isabout 90° F. As a further safety feature, a second redundant temperaturesensor 94 is provided in bath 32 at a location different from that ofsensor 84. If the temperature measured by sensor 94 exceeds a secondpredetermined value, which is approximately 5° F. higher than the firstpredetermined value associated with sensor 84, pump 36 and conveyor 20are again disabled. In this manner, should sensor 84 fail, sensor 94serves as a back up. In both instances, resumption of activity cannotoccur until the bath temperature drops sufficiently, or until thetemperature control is manually overridden at control panel 92.

One or two temperature sensors 96 are positioned above conveyor 20 andtop sprayers 34. Sensors 96 monitor the temperature of the vaporoverlying bath 32, and of the liquid being emitted by sprayers 34. Ifthe temperature detected by either of sensors 96 exceeds a predeterminedvalue, such as 140° F., a signal is sent to control panel 92, whichopens a valve 98, releasing carbon dioxide from a cylinder 100 beneathbath 32 into the space in cavity 27 overlying bath 32. Thus, if thetemperature of the vapors overlying bath 32 begins to approach the flashpoint thereof, carbon dioxide is released to suppress any potentialfire, and to reduce the vapor temperature.

Safety shut offs are also provided in conjunction with scrubber means 56to prevent the release of corrosive vapors or odors into the atmosphere.A water flow detector 62 is disposed in each of ducts 44 and 46 justbelow washing means 58. If insufficient water, below a predeterminedthreshold, is flowing from washing means 58 to cleanse scrubber means56, a signal is provided to control panel 92 which disables conveyor 20and pump 36 to stop the washing process. A similar function is providedby an air flow detector 64, one of which is positioned in each of ducts44 and 46. If insufficient air flow, below a predetermined threshold, isdetected from cavity 27 by detector 64 through either of ducts 44 or 46,a signal is sent to control panel 92 which again disables conveyor 20and pump 36 to stop the washing process. In this manner, properventilation is maintained during operation of washing apparatus 12, andthe release of odors or vapor through inlet 18 or outlet 22 due to thefailure of fan 48 to adequately vent cavity 27 is prevented. Also,proper washing of scrubber means 56 is maintained. Typically, thethreshold for water flow detector 62 is 0.6-1.0 gallons per minute,while the threshold for air flow detector 64 is 200-300 cubic feet ofair per commercially available, acceptable water flow detector is anAFS-4 series switch sold by IMO Industries, Gems Sensor Division. Acommercially available, acceptable air flow detector is a Model 530airflow switch sold by Dwyer.

In addition to the foregoing, if for any reason the operator wishes tostop the rinsing or washing process, manual stop buttons 100 areprovided on control panel 92. Furthermore, a button is provided at aremote location to permit the operator to manually release carbondioxide, if flames are sited.

Unloading conveyor assembly 14 will now be described with particularreference to FIGS. 1-3. Conveyor assembly 14 automatically transferswashed printed circuit boards from conveyor 20 to rinsing apparatus 16.Conveyor assembly 14 includes a conveyor 120 mounted within a frame 122.Conveyor 120 rests on lip 124 of hood 78 of apparatus 12 at one end andon support 125 extending from apparatus 16. A pan 127 resides underneathconveyor 120 to catch any water thereon and conduct it to apparatus 16.A lip 129 on the end of pan 127 facing apparatus 12 prevents any wateron conveyor 120 from being splashed onto conveyor 20. The ends ofconveyor 120 are spaced from adjacent ends of conveyors 20 and 134, butare closely adjacent thereto. Preferably, conveyor 120 extends into hood78 and into inlet 150.

Conveyor 120 may be an open mesh conveyor, similar to conveyor 20 toprevent the transport of washing compound from apparatus 12 or thetransport of water from apparatus 16 to apparatus 12. Conveyor 120 isdisposed at an angle with respect to the horizontal, such that theportion thereof closest to outlet 22 of apparatus 12 and which receivesboards from conveyor 20 is higher vertically than the portion thereofclosest to rinsing apparatus 16 which delivers boards to apparatus 16.Should water be deposited on conveyor 120 by rinsing apparatus 16, thiswater will tend to run downhill under the influence of gravity towardsrinsing apparatus 16, and not towards washing apparatus 12. In thismanner, any flow of water or water vapor from rinsing apparatus 16 towashing apparatus 12 along assembly 14 is eliminated, and all water onassembly 14 is returned to apparatus 16. The angle that conveyor 120forms with respect to the horizontal should exceed 5°, and an angle of5°-10° is preferred.

Assembly 14 is either exposed to permit air to circulate around it, asshown in FIGS. 1-3, or it is housed separately and distinctly from bothwashing apparatus 12 and rinsing apparatus 16.

If a housing is provided surrounding assembly 14, such a housing shouldhave openings at either end thereof to permit conveyor 120 and theboards to pass therethrough. However, a housing surrounding assembly 14is not necessary, as the boards are almost dry when reaching conveyor120, and emission of the odoriferous vapor into the atmosphere is not aserious problem. In addition, any such housing does not have much, ifany, impact on the transfer of water vapor from rinsing apparatus 16 towashing apparatus 12.

Conveyor assembly 14 separates the rinsing apparatus 16 sufficientlyfrom the washing apparatus 12, so that no water from rinsing apparatus16 finds its way into bath 32. As previously indicated, small amounts ofwater can cause the terpene in bath 32 to gel, interfering with its freeflow through sprayers 34. If sufficient gel forms in bath 32, it must bediscarded, and a new bath utilized. Typically, a single bath 32 can beused for several months of operation before it must be replaced, becauseof the ability of the terpene compounds to dissolve large quantities ofrosin flux. Because of the expensive nature of the bath, it is highlyundesirable to have to change the bath at more frequent intervals thanis necessary. Assembly 14 should be sufficiently long to space washingapparatus 12 from rinsing apparatus 16 an amount necessary to minimizethe transfer of any water vapor or water from rinsing apparatus 16 tobath 32. It has been found that a typical distance which is sufficientto perform this function is about 24 inches.

Rinsing apparatus 16 will now be described with particular reference toFIGS. 1-3. Rinsing apparatus 16 rinses the washing compound, such as aterpene compound, from the boards and completes the removal of rosinfluxes. Disposed within housing 136 of apparatus 16 is a water bath 128,a pump 130, sprayers 132, conveyor 134, air knives 154 and dryer 156.Conveyor 134 is an open mesh conveyor which permits water from sprayers132 to return to bath 128 after rinsing of the boards. Conveyor 134transports the boards through apparatus 16 from an inlet 150 to anoutlet 144. Sprayers 132 are similar to sprayers 34, and are disposedboth above and below conveyor 134. Sprayers 132 comprise an array ofnozzles 138 which cover the entire width and a substantial portion ofthe length of conveyor 134 with a water spray. In one embodiment,sprayers 132 comprise a plurality of generally parallel tubes 140 whichextend transversely of the direction of movement of conveyor 134, eachof which contain a plurality of nozzles 138. Typically, nozzles 138spray the boards at an angle with respect to the vertical and with afan-shaped spray, to flush fluxes and washing compounds from the spacesbetween the components and the board surface. The number of nozzles 138and tubes 140 is selected such that the entire width and a desiredportion of the length of conveyor 134 is covered by spray. The exactnumber of each depends upon the angle of spray. In one embodiment, 14tubes are used in conjunction with 3 nozzles per tube. Typically,nozzles 138 are disposed at an angle 165 of zero to 20° with resect tothe vertical, with 15°-20° being preferred. The spray angle 167 ispreferably about 120°.

Preferably, deionized or tap water is used in water bath 128. The waterbath can comprise two or more stages, or it can comprise a single stage,as desired. In addition, either recycled or fresh water can be used. Apreferred structure is shown in FIGS. 2 and 3. This embodiment comprisesa three step rinsing process in which sprayers 132 are divided intothree groups, initial rinse sprayers 148, secondary rinse sprayers 146and final rinse sprayers 142. Sprayers 148 are disposed adjacent inlet150, while sprayers 142 are disposed between inlet 150 and air knives154. Bath 128 is segmented into three sections, 128A, 128B and 128C bywalls 127 and 129. Section 128A recovers water from sprayers 142, whilesection 128B recovers water from sprayers 146. Water from sprayers 148is collected by section 128C. Pump 131 pumps collected water fromsprayers 146 in section 128B to sprayers 146, while pump 130 pumps watercollected from sprayers 148 in section 128C to sprayers 148. Fresh wateris supplied to sprayers 142 and supplies section 128A. Water in section128A overflows wall 129 to supply section 128B, and water in section128B overflows wall 127 to supply section 128C. Pipe 171 drains waterfrom section 128C when the water level exceeds that of top 173 of pipe171. In this manner, the dirtiest water is used when the boards enterrinsing apparatus 16 at inlet 150, while the cleanest water is used justprior to air knives 154. The flow of water into and out of rinsingapparatus 16 obviously should be equal, and typically is in the range ofabout 4 to 5 gallons per minute. It should be understood that additionalgroups of sprayers can be provided, so long as the cleanest water isintroduced in the sprayers most closely adjacent outlet 144. Instead ofthree rinse steps, 4, 5, 6 or more rinse steps may be used, with thewater recovered from each step being recirculated to the sprayers in theimmediately preceding step.

Although not necessary, typically a heater or heaters 152 is provided toheat the water supplied to sprayers. A preferred temperature is about120° F. A heater 155 may also be incorporated into baths 128B and 128Cto maintain an elevated temperature in the rinse water used for sprayers146 and 148. Heating the rinse water assists in the removal of thecleaning compound and enhances drying.

In a preferred embodiment, an air knife 154, or a plurality of airknives 154 is provided between sprayers 142 and outlet 144. Preferably,air knives 154 are disposed between openings 162 and outlet 144. Airknives 154 assist in mechanically removing free standing water. Airknives 154 may be identical to air knife 30 and comprise a tube having aplurality of nozzles to which air is supplied under pressure. Eitherheated or non-heated air may be supplied to air knife 154, althoughtypically, air heated by heater 157 is utilized. Heater 157 can beeither an air heater or it can be part of the blower 177. Heater 157elevates the board temperature in preparation for later drying withinhousing 153. A dryer 156 is provided at outlet 144 to dry the boards andcomponents. Although dryer 156 is not necessary, it assists in the finalremoval of water. Typically, dryer 156 is an infrared heater and isdisposed within a portion of housing 136. The board enters dryer 156after leaving air knife 154 and the remaining water is evaporated andthe board is dried. The temperature of dryer 156 should be adjusted toallow for various board configurations.

A baffle 160 is provided at inlet 150 to minimize the escape of waterand water vapor from the interior of rinsing apparatus 16. Baffle 160 istypically a flexible curtain suspended from its top edge which has beensegmented into a plurality of vertically extending strips and which cabe easily pushed aside by the boards as they enter through inlet 150.This curtain maybe composed of any flexible material, but typicallyViton is used.

At least two exhaust ducts 158 are provided having openings 162 withinhousing 136, one opening 162 adjacent inlet 150 and the other opening162 adjacent outlet 144. Ducts 158 are coupled to fan 164 which exhaustsair from the interior of housing 136. In this manner, a negative airpressure is created at both inlet 150 and outlet 144 to minimize theescape of water and water vapor from the interior of housing 136.

In a preferred embodiment, as shown in FIGS. 6 and 7, windows 104 areprovided in the top surface of washing apparatus 12, as shown in FIGS. 2and 3. Windows 104 typically are affixed to housing 26 along one edge byhinge 106 which permits them to be pivoted from an open to a closedposition. Access to the interior of housing 26 can be gained by openingone of the windows. Locks 108 secure windows 104 against housing 26 in aclosed position. Locks 108 are provided in conjunction with each window104 along an edge opposite of the location of hinge 106. A preferredembodiment of locks 108 is shown in FIGS. 6 and 7. Typically, each lock108 includes a manually operable bolt 110, threaded onto window 104, anda cooperatively threaded nut 112 disposed on the outer, upper surface ofhousing 26 along frame 114 of window 104. Windows 104 are locked bythreading bolt 110 into nut 112. A safety feature is provided whereinwashing apparatus 12 can not be operated unless windows 104 are locked.A switch 116 is disposed within nut 112, and senses whether tip 118 ofbolt 110 has penetrated to the location of switch 116. Once all switches116 in all locks 108 have been tripped by the passage of tips 118 ofbolts 110, power is supplied to apparatus 10 through control panel 92.Typically, switch 116 is positioned at the bottom of nut 112, so thatall windows 104 are at least partially secured to respective windowframes 114 during PG,33 operation of apparatus 10. Switch 116 typicallyis a reed-type switch, which includes a magnet 127 in tip 118 and asensor 129 in nut 112. Similar locks may also be provided in conjunctionwith windows in the top of rinsing apparatus 16.

The operation of apparatus 10 of this invention will now be describedwith particular reference to FIGS. 1-3. Typically, apparatus 10 isdisposed in an in line relationship with a soldering apparatus, such asa VITRONICS infrared solder reflow apparatus for mounting surfacemounted devices to printed circuit boards. The conveyor 77 for this, orsome other type of soldering apparatus is partially shown in FIG. 1.After the soldering process has been completed, printed circuit boards170 are transferred across a gap between conveyor 166 onto conveyor 20at opening 80 of hood 76. These printed circuit boards 170 are thentransferred by conveyor 20 into and through housing 26. These boardsfirst pass through hood 76, and beneath flame detector 90. If flamedetector 90 detects a flame or excess heat on a board 170 passingtherebeneath, the material within flame detector 90 is melted, breakingthe circuit passing therethrough, and disabling the apparatus.Otherwise, the printed circuit board passes into the interior of housing26.

During this time, fan 48 is creating a negative pressure at opening 80,drawing air into the interior of housing 26 and exhausting it, after theair passes through scrubbers 50. Liquid and solid particles are removedfrom the exhaust air stream by scrubbers 50, and are passed to drain 60by washers 58. If no water is flowing within washers 58, water flowdetector 62 disables the machine. Similarly, if no air is flowingthrough scrubbers 50, air flow detector 64 disables the machine,stopping conveyor 20 and pump 36.

Printed circuit boards 170 pass beneath sprayers 34 where they arewashed for a desired period of time by a terpene compound emitted bynozzles 42. Each tube 40 washes the board in sequence, and the washingtime is determined by the conveyor speed and the number of tubes 40. Thecompound emitted by nozzles 42 strikes the board with sufficient forceand at a sufficient angle with respect to the vertical to remove anyrosin flux, and to be forced into the narrow spaces between thecomponents mounted on the board, and the board surface. The material inthe bath typically is a terpene compound, mixed with a surfactant aspreviously described. A preferred terpene compound is sold under thetrademark BIOACT EC-7.

As board 170 approaches outlet 22, it passes beneath air knife 30 whichdirects a high velocity air stream onto the board to remove excessamounts of the terpene compound, but which does not remove all of it,leaving the board slightly damp. The airstream preferably is disposed atan angle with respect to the vertical. The board then passes throughhood 78 and over a gap between conveyor 20 and conveyor 120 ontounloading conveyor assembly 14. Fan 48 again creates a negative airpressure at opening 82 drawing air into the interior of housing 26, toprevent the escape of any vapors or droplets through opening 82 as theboard departs. The board then travels downwardly toward rinsingapparatus 16 on conveyor assembly 14.

As the board approaches rinsing apparatus 16 on conveyor 120, any waterwhich escapes from the interior of rinsing apparatus 16 will condenseand run down conveyor assembly 14 back into rinsing apparatus 16. Also,since most of the terpene compound solution has been removed from theboard prior to passing through outlet 22, very little terpene compoundescapes into the surrounding air.

The board passes onto conveyor 134 across the narrow gap betweenconveyor 120 and conveyor 134. Baffle 160 is pushed aside by the boardas it enters apparatus 16. While baffle 160 is sufficiently flexible toallow a board to pass therebeneath, gravity returns it to its originalposition, effectively closing inlet 150 to prevent the escape of waterand vapor. Fan 164 draws air in through inlet 150 and into duct 158,further inhibiting the escape of water or water vapor through inlet 150.The board then passes beneath sprayers 148, 146 and 142 in sequence.Each of sprayers 148, 146 and 142 extends across the entire width ofconveyor 134, and each fully involves the board with its water spray.The spray from the nozzles 138 associated with each of these sprayers issufficiently strong and disposed at a sufficient angle with respect tothe vertical to wash down the board and remove solder fluxes, and toforce the water beneath the components on the board. The wetting orwicking action of the surfactant assists in drawing water beneath thecomponents to cleanse the small spaces thereunder. The water supplied tosprayers 148 is drawn from section 128C, conducted to sprayer 148, andis recovered by section 128C, after which the water is drained by pipe171. The board then passes beneath sprayers 146. Water is drawn fromsection 128B, passed through sprayers 146 to provide a second rinse, andis recovered by section 128B. Afterward, water flows over wall 127 intosection 128C. Finally, the board passes beneath sprayers 142 which arethe final stage rinse. Clean water is used, such as tap water. Wateremitted by sprayers 142 is collected by bath 128A, and afterward, waterflows over wall 129 into section 128B. Preferably, this water is heatedby heater 152 prior to being conducted to sprayers 142. The board thenpasses beneath air knife 154 which removes most of the free standingwater and remaining dissolved rosin fluxes from the board. Finally, ifdesired, the board passes beneath dryer 156 after it exits outlet 144and passes into housing 153. The board is now dried and ready for use.

Because of the highly aggressive nature of most terpene compounds, thecomponents of apparatus 10 must be formed of a material which would notbe affected by these compounds. There are a variety of materials whichare compatible with terpene compounds, and which may be used to formsprayers 34, housing 26, conveyor 20 and other components of washingapparatus 12 which are directly exposed to the terpene compounds andtheir vapors. Various types of Teflon® as well as polyvinyl difluorideare plastics which can be used to form these components. Stainless steelmay also be used, and is the preferred component, because it not onlywithstands the terpene compounds, but also is unaffected by the waterrinse. The tubing used in the apparatus can be stainless steel, bronze,copper or galvanized steel.

The foregoing apparatus is capable of removing rosin solder fluxes fromprinted circuit boards and other like assemblies using terpenecompounds. Such apparatus is more effective than prior art apparatuswhich use chlorinated hydrocarbon and chlorofluorinated compounds, andperforms better than most aqueous cleaning apparatus. Studies have shownthat terpene compound cleaning leaves less residue is left on thesurfaces of the boards and components. Furthermore, in contrast to priorart apparatus, this apparatus does not create any hazard to theenvironment, as the by-products of the cleaning process are fullybiodegradable.

In view of the above description, it is likely that modifications andimprovements will occur to those skilled in the art which are within thescope of this invention. The above description is intended to beexemplary only, the scope of the invention being defined by thefollowing claims and their equivalents.

What is claimed is:
 1. Apparatus for cleaning devices using a fluidsubstance, said apparatus comprising:first means for conveying devicesfrom a first end thereof to a second end; means disposed at a locationbetween said first end and said second end of said first conveying meansfor washing devices with a first fluid substance; second means forconveying devices from a first end thereof to a second end thereof, saidsecond conveying means receiving devices at said first end thereof fromsaid second end of said first conveying means, said first end of saidsecond conveying means being spaced from and unconnected with saidsecond end of said first conveying means; means disposed between saidfirst end and said second end of said second conveying means for rinsingdevices with a second fluid substance; and means for preventing vaporsassociated with said first fluid substance from becoming ignited, saidpreventing means comprising:a temperature sensor disposed adjacent saidfirst conveying means; a source of a non-flammable gas; and meansrepsonsive to said temperature sensor for releasing said gas when saidtemperature sensor detects a temperature above a predetermined value butbelow the temperature at which the vapors would ignite.
 2. Apparatus forcleaning devices using a fluid substance, said apparatuscomprising:first means for conveying devices from a first end thereof toa second end; means disposed at a location between said first end andsaid second end of said first conveying means for washing devices with afirst fluid substance; second means for conveying devices from a firstend thereof to a second end thereof, said second conveying meansreceiving devices at said first end thereof from said second end of saidfirst conveying means, said first end of said second conveying meansbeing spaced from and unconnected with said second end of said firstconveying means; means disposed between said first end and said secondend of said second conveying means for rinsing devices with a secondfluid substance; a bath associated with said first conveying means forcontaining the first fluid substance used for washing of devices on saidfirst conveying means; means for circulating the first fluid substancefrom said bath to said washing means; means for cooling said bathcontaining the first fluid substance; a temperature sensor for detectingthe temperature of said bath; and means responsive to said temperaturesensor for controlling said cooling means to maintain a temperature ofsaid bath below a predetermined temperature.
 3. Apparatus for cleaningdevices using a fluid substance, said apparatus comprising:first meansfor conveying devices from a first end thereof to a second end; meansdisposed at a location between said first end and said second end ofsaid first conveying means for washing devices with a first fluidsubstance; second means for conveying devices from a first end thereofto a second end thereof, said second conveying means receiving devicesat said first end thereof from said second end of said first conveyingmeans, said first end of said second conveying means being spaced fromand unconnected with said second end of said first conveying means;means disposed between said first end and said second end of said secondconveying means for rinsing devices with a second fluid substance; andmeans disposed above said first conveying means at said first endthereof and spaced from said washing means for detecting the presence ofa flame on a device before the device is sprayed with the first fluidsubstance by said washing means, whereby no first fluid substance issprayed on the device before the device is inspected by said detectingmeans.
 4. Apparatus for cleaning devices using a fluid substance, saidapparats comprising:first means for conveying devices from a first endthereof to a second end; means disposed at a location between said fistend and said second end of said first conveying means for washingdevices with a first fluid substance; second means for conveying devicesform a first end thereof to a second end thereof, said second conveyingmeans receiving devices at said first end thereof from said second endof said first conveying means, said first end of said second conveyingmeans being spaced from and unconnected with the second end of saidfirst conveying means; means disposed between said first end and saidsecond end of said second conveying means for rinsing devices with asecond fluid substance; a housing at least partially surrounding saidfirst conveying means; means or exhausting gases within said housing andfor drawing ambient air into said housing; scrubber means disposed insaid exhausting and drawing means for removing pollutants from airexhausted from said housing, said scrubber means comprising:airpermeable pollution removal means for removing liquid and solidcomponents of the gases exhausted from said housing; and means forwashing said pollution removal means to remove pollutants therefrom. 5.Apparatus for cleaning devices using a fluid substance, said apparatuscomprising:first means for conveying devices from a first end thereof toa second end; means disposed at a location between said first end andsaid second end of said first conveying means for washing devices with afirst fluid substance; second means for conveying devices from a firstend thereof to a second end thereof, said second conveying meansreceiving devices at said first end thereof from said second end of saidfirst conveying means, said first end of said second conveying meansbeing spaced from and unconnected with said second end of said firstconveying means; means disposed between said first end and said secondend of said second conveying means for rinsing devices with a secondfluid substance; a housing at least partially surrounding said firstconveying means; at least one openable window disposed in a wall of saidhousing; means for locking said window in a locked condition; means forsensing whether said window is in said locked condition; and meansrepsonsive to said sensing means for disabling said first conveyingmeans if said window is not in said locked condition.
 6. Apparatus forremoval of solder rosin fluxes from printed circuit boards, saidapparatus comprising:first means for conveying printed circuit boardsfrom a first end of said first conveying means to a second end of saidfirst conveying means, said first conveying means being adapted toreceive printed circuit boards at said first end thereof from asoldering apparatus; a bath associated with said first conveying meansand containing first fluid substance; means for washing printed circuitboards disposed on said first conveying means with said first fluidsubstance; means for recovering said first fluid substance after washingof printed circuit boards and returning said first fluid substance tosaid bath; means for circulating said first fluid substance from saidbath to said washing means; second means for conveying printed circuitboards from a first end thereof to a second end thereof, said first endof said second conveying means being adapted to receive printed circuitboards from said second end of said first conveying means, said firstend of said second conveying means being spaced from and unconnected tosaid second end of said first conveying means; means for rinsing printedcircuit boards disposed on said second conveying means with a secondfluid substance; a baffle disposed between second end of said firstconveying means and said first end of said second conveying means forpreventing the second fluid substance from coming in contact with saidfirst conveying means and said bath; and means for preventing ignitionof vapors of said first fluid substance.